This program is aimed at discovering how ATP hydrolysis is coupled to the myosin-actin assembly to produce mechanical thrust. Two projects - one employing correlation spectroscopy and one employing relaxation methods - examine whether ATPase is coupled to repetitive cross-bridge motion and seek to characterize the motion. There are also efforts in ascertaining morphology from X-ray scattering and examining the role of myosin light chain phosphorylation. The supplement adds a component concerned with the detailed chemistry of the transducing particle itself (S-1 piece of the myosin molecule), and those interactions of the transducer that get amplified into cross-bridge motion.